问根据用户在页面上的位置更改jQuery

EN

    $(document).ready(function(){
  var targetOffset = $('header').offset().top + $('header').height();

  var $w = $(window).scroll(function(){
      if ( $w.scrollTop() > targetOffset ) {
          $("#nav").css('background-color', 'rgba(35,46,63,1)');
      } else {
        $('#nav').css('background-color', 'rgba(35,46,63,0)');
      }
  });
});

nav {
    background-color: rgba(35,46,63,0);
    transition: background-color 200ms linear;
    position: fixed;
    left: 0;
    right: 0;
    padding: 25px;
    z-index: 1;
    box-shadow: 0px 0px 0px rgba(0,0,0,0);
}

nav > .wrapper {
    overflow: hidden;
}

nav > .wrapper > li.nav-logo {
    list-style: none;
    font-weight: 600;
    padding: 0px;
    border-top: 1px solid rgba(0,0,0,0);
}

nav > .wrapper > li.nav-logo > a {
    color: #DDDDDD;
    text-decoration: none;
}

nav > .wrapper > li.nav-logo > a > img.left {
    width: 5%;
    display: inline-block;
    float: left;
}

nav > .wrapper > ul.right {
    list-style: none;
    float: right;
}

nav > .wrapper > ul > li {
    display: inline-block;
    list-style: none;
    font-weight: 400;
    font-size: 0.9em;
    padding: 15px;
    border-bottom: 1px solid rgba(0,0,0,0);
    border-radius: 6px;
    vertical-align: middle;
    transition: all 0.3s ease;
}

nav > .wrapper > ul > li > a {
    color: #FFFFFF;
    text-decoration: none;
    transition: all .3s ease;
}

nav > .wrapper > ul > li > a:hover {
    color: white;
    text-decoration: none;
}

<nav id="nav">
    <div class="wrapper">
        <li class="nav-logo"><a href="#"><img class="left" src="assets/images/ugn-logos/single-ugn-logo.png" alt="ugn-logo"></a></li>
        <span class="nav-btn"><i class="icon-menu"></i></span>
        <ul class="right">
            <li><a href="index.html">Home</a></li>
            <li><a href="shared-hosting.html">Shared Hosting</a></li>
            <li><a href="vps.html">VPS</a></li>
            <li><a href="minecraft.html">Minecraft</a></li>
            <li><a href="#">Contact</a></li>
        </ul>
    </div>
</nav>